1. Field of the Invention
The present invention pertains to materials that may be used to seal punctures in pneumatic tires, and, more particularly, to sealant compositions that contain a puncture filler material and a liquid carrier agent. Still more specifically, the invention pertains to low-viscosity sealant compositions that are introduced into inner tubes for rapidly sealing punctures as they occur, in order to prevent the occurrence of flat tires.
2. Statement of the Problem
Automotive tire sealant and/or ballasting compositions typically have a high apparent viscosity due to the need to resist escaping air and the need to provide a balanced uniform thickness of sealant on the tire wall where punctures occur. Kent et al, U.S. Pat. No. 4,101,494, teaches a ballasting composition having an apparent viscosity of from 1000 to 2200 centipoise at 100.degree. F. This ballasting composition contains asbestos fibers and a polyvinyl alcohol, as well as an optional ethylene glycol antifreeze portion. Tibbals, U.S. Pat. No. 3,747,660, teaches a thixotropic tire ballasting composition that consists essentially of a gel-forming clay and an alkali metal hexametaphosphate. Kitamura et al, U.S. Pat. No. 4,607,065, teaches a sealant composition including butyl rubber, a tackifier, an acrylol or methacrylol group-containing a polymerization unsaturated compound, a filler, and a photopolymerization initiator. The filler may include glass fibers, clay, and silica. These high-viscosity compositions are useful in tubeless automotive tires, which operate at elevated temperatures resulting from high rpm and frictional contact with the pavement. A major problem exists with these compositions in that they contain ingredients which are potentially very hazardous to human health. Additionally, the butyl rubber-containing sealants are typically sprayed into a fixed position on the outer tire wall, but inner tubes cannot receive the sealants in this manner.
Prior tire sealant mixtures of the type that may be applied through a valve stem opening have traditionally been used only in Schrader-type valves, i.e., those having a spring-biased valve core that may be completely removed from the valve air inlet opening by unthreading the core from the threaded interior of the valve stem where it is seated. The Schrader valves are in widespread use on automobiles and probably a majority of bicycles. Even so, many bicycles have a European style Presta-type valve, which has a narrower valve stem interior than does the Schrader valve, and relies upon air pressure (not spring bias) for sealing. Tire sealant mixtures that include a viscous mixture of liquid and fibers typically clog Presta valves.
A commercially available viscous-fiber tire sealant composition, SLIME.sup.1 from Access Marketing of Shell Beach, Calif., contains propylene glycol, man-made fibers, a corrosion inhibitor, and a biocide. These ingredients are typical of most commercially available fibrous bicycle tire sealants. This liquid composition is sold as a bicycle tire sealant, and is pumped into tires through a Schrader-type valve stem opening; however, the composition usually clogs the Presta-type valve cores and, as a practical matter, cannot be used to seal inner tubes having these types of valve cores. Furthermore, the mixture fails to seal many types of punctures in an instantaneous manner, and significant pressure drops are often observed after the puncture occurs. While the fibrous mixture has a lower apparent viscosity than do the automotive sealants and ballasting compositions that are discussed above, the apparent viscosity is still relatively high. FNT .sup.1. SLIME is a trademark of Access Marketing of Shell Beach Calif.
There remains a need for an environmentally compatible prophylactic sealant composition that is effective for sealing tire and inner tube punctures without significant pressure loss.